The present invention relates to a device for compacting soil, the device including at least one movable drum which is in operative connection with eccentric exciter shafts that are arranged parallel to the drum axis and rotate in synchronism so that the drum selectively exerts primarily a dynamic shearing force or a pressure force on the soil.
Such a compacting device is disclosed in EP-B 0,053,598. It includes two exciter shafts which rotate in the same sense of rotation but are shifted in phase by 180 .degree.. In this way, the vertical forces generated by the exciter shafts compensate one another while the oppositely directed horizontal forces generate a torque on the drum about the drum axis. This torque causes a predominant shear force to act on the soil which is of advantage when compacting thin layers of soil.
In the majority of cases, the soil must also be compacted in depth. For this purpose it is necessary for the drum to exert primarily a pressure force on the soil. To accomplish this, the phase difference between the two exciter shafts in the mentioned device must be reduced from 180.degree. to 0.degree.. The excitation forces generated by the eccentric masses then rotate in the same sense and in the same phase so that, depending on the angular position of the exciter shafts, vertical pressure forces are also exerted on the soil.
Based on this state of the art, applicant's tests have shown the following:
Although the generation of pure torques about the drum axis leads to a certain reduction of vibration stresses on the vehicle structure, it creates, on the other hand, a slip between the drum and the soil surface. This results in traction problems if the compaction drum must be used on a downhill or an uphill slope. This problem is augmented if the described system is employed in compaction devices employing two oscillating drums because then no rubber wheels are available to guide the compactor.
Additionally, bituminous materials may develop undesirable waves and smoothing of the surfaces.
Finally, the structural expenditures are also rather high because the exciter shafts must be mounted far away from the drum axis in order to generate the desired torque and because additionally the one exciter shaft must be provided with adjustable flyweights.